A mass flow controller (MFC) is a device that sets, measures, and controls the rate and amount of fluid passing through the device. The fluid may be of any type, including but not limited to gas, vapor, or liquid, by way of example. These devices are typically designed and calibrated to control with high precision the flow of fluid within a predefined range of flow rates. Some manufacturing processes, such as semiconductor manufacturing, require precise control of the rate of fluid flow and the amount (mass) of gases and vapors that are being delivered to a process chamber or tool.
Applications of MFCs include, but are not limited to, metering of precise amounts of gases and vapors flowing into a process chamber for subsequent deposition on work pieces, dry etching to remove material, ion and plasma beams used in the semiconductor and pharmaceutical industries, etc. In many of these applications, accuracy of fluid flow rates and fluid mass is important in order to ensure optimal results.
The control valve is an important component in an MFC. It regulates the mass flow rate of the fluid, by varying the degree or amount by which the valve is open, according to the control command set by the MFC. The minimum electric current in the valve actuator which causes the valve plug to begin to open is commonly referred to as the valve cracking current or the valve threshold current.
To update the valve cracking current, methods have been used that require pressure information, i.e. require an embedded pressure sensor in the MFC to monitor the operating condition. Not all MFCs, however, include an embedded pressure sensor, making it difficult for such MFCs to update the valve cracking current when such methods are used. Also, these methods may not correctly predict the valve cracking current if the valve is drifted.
Systems and methods that allow the valve cracking current to be correctly determined and updated, without requiring pressure information, is desirable, and would improve control performance of MFCs at different pressures.